The present invention relates to an apparatus for video playback for decoding video data encoded by a predetermined encoding system and encoding the decoded video data into a signal for displaying on a screen of a display device and a method thereof.
When video data is recorded on a record medium, such as a DVD (Digital Video Disk, or Digital Versatile Disk) or when video data is distributed on the internet, the data is often encoded using the MPEG-2 (Moving Picture Expert Group Phase 2) digital compression standard. To play back or reproduce MPEG-2 data, an MPEG-2 decoder, for returning the data to the original video data by decoding the data, is required. Further, an NTSC (National Television System Committee) encoder for encoding the video data decoded by the MPEG-2 decoder into a signal capable of being output to a television is required.
FIG. 4 shows an example of the structure of a video playback apparatus 10 having a playback function capable of decoding an MPEG-2 encoded data stream. A NIM (Network Interface Module) 12 is connected to a communication line to control transmitting and receiving data. For example, when a satellite communication line is used, a parabolic antenna is connected to the NIM 12. The Internet may also be accessed by connecting a telephone line to the NIM 12. An MPEG-2 TS (Transport Stream) obtained by multiplexing a plurality of MPEG-2 data and associated data such as a program list is transmitted in a satellite broadcast.
Each data included in the MPEG-2 TS is separated by an MPEG-2 TS demultiplexer 20. One MPEG-2 data is extracted out of a plurality of MPEG-2 data. An MPU (Microprocessor Unit) 24 specifies the MPEG-2 data to be extracted by the demultiplexer 20. The data extracted by the demultiplexer 20 is transmitted to an MPEG-2 decoder 22 to be decoded. The program list is also extracted by the demultiplexer 20 to be transmitted to MPU 24.
The video data decoded by the MPEG-2 decoder 22 is transmitted to an NTSC encoder 32 through a graphic processor 30. The graphic processor 30 performs display processing for characters and images processed by MPU 24. For example, display processing is performed to superimpose a program list on the data decoded by the MPEG-2 decoder 22. The data transmitted to the NTSC encoder 32 is encoded into, for example, an NTSC signal. The data encoded into the NTSC signal is supplied to a video input terminal of a television (not shown).
Nowadays, a web-site browsing function is often added to video playback apparatus. Since the graphic processor 30 performs display processing of Web pages, a higher-speed graphic processor becomes necessary. In addition, MPEG-2 decoders adaptable to high-definition television broadcasts or MPEG-2 decoders capable of simultaneously decoding a plurality of MPEG-2 data may be used. To provide a system configuration suitable for such requirements, as shown in FIGS. 4 and 5, in many cases, the MPEG-2 decoder 22, MPU 24, and the MPEG-2 TS demultiplexer 20 are integrated on a single chip (14), and the processor 30 and the encoder 32 are integrated on a single chip (16).
A typical example of a data format of video data transmitted from the MPEG-2 decoder 22 to the NTSC encoder 32 is ITU-R (International Telecommunication Union-Radio Communication Sector) Recommendation BT.601. The ITU-R BT.601 defines the type of coding of color information, such as RGB, YUV4:4:4, and YUV4:2:2. In this case, RGB is a coding type indicating color information by red (R), green (G), and blue (B). YUV is a coding type indicating color information by brightness (Y), color difference in red (U), and in blue (V).
For YUV4:4:4, the ratio of the number of samples of brightness (Y), color difference in red (U), and color difference in blue (V) is equal. For YUV4:2:2:, the ratio of the number of samples of brightness (Y), color difference in red (U) and color difference in blue (V) is 2:1:1. The coding type YUV4:2:2 of ITU-R BT.601 is hereinafter referred to as BT.601 (YUV4:2:2).
The data format also defines the type of the order of data transmission. In the case of the recommendation BT.601 (YUV4:2:2), some types are defined for the order of data transmission, such as VYUY and UYVY. In the case of the BT.601 (RGB), some types are defined for the order of data transmission, such as GBR and BRG.
Further, the data format defines the bus width used for data transmission, such as 8 bits and 16 bits.
As shown in FIGS. 6(a) and 6(b), the data format setting is stored in a format register FR22 included in the MPEG-2 decoder 22, a format register FR30 included in the graphic processor 30, and a format register FR32 included in the NTSC encoder 32.
As shown in FIG. 6(b), data xcex1 indicating the type of coding, such as the BT.601 (RGB), the BT.601 (YUV4:4:4), and the BT.601 (YUV4:2:2), data xcex2 indicating the order of data transmission, such as VYUV, UYVY, GBR, and BRG, and data xcex3 indicating the bus width for data transmission, such as 8 bits and 16 bits, are stored, respectively, in the registers FR22, FR30, and FR32.
Table 1 shows an example of data format types which can be used in the MPEG-2 decoder 22.
Table 2 shows an example of data format types which can be used in the graphic processor 30 and the NTSC encoder 32.
One of the types defined in both Table 1 and Table 2 is selected for each item. For example, as shown in FIG. 6(c), data xcex1 can be set to YUV4:2:2, data xcex2 can be set to UYVY, and data xcex3 can be set to 8 bits. The setting shown in FIG. 6(c) are stored in a memory element (not shown), such as a ROM (Read Only Memory) or a flash memory so that MPU 24 may set a data format based on the contents of this memory. Data format setting usually remains fixed to only one kind of data format.
The MPEG-2 decoder 22, the graphic processor 30, and the NTSC encoder 32 work based on the respective setting of the registers FR22, FR30, and FR32. For example, as shown in FIG. 7, when the bus width is 8 bits, only the solid line portion of wiring 42 is used, and when the bus width is 16 bits, both the solid line portion and broken line portion of the wiring 42 are used. Further, a controlling method for data transmission is also changed depending on the setting of the registers FR22, FR30, and FR32 since YUV4:4:4 and YUV4:2:2 differ in data ratio of brightness Y and color differences UV, and the bus widths of 8 bits and 16 bits differ in amount of data transferred at one time.
The video data that is provided as output from the video playback apparatus 10, shown in FIG. 4, to a television can be copied using a general video deck. However, copying of video data that is output to the television can be prevented by using an NTSC encoder with Macrovision (trademark) copy protection, which is an example of a copy protection method.
It is, however, possible to extract video data in chips 14 and 16 shown in FIG. 5 from the wiring 42, via conductive holes 44, and chip terminals 46 for connecting the chips 14 and 16. Since the video data extracted at these points is digital data, copying is easy and in addition, the copied video data is not deteriorated. Usually, particular anticopy steps are not taken because these chips 14 and 16 are located within the video playback apparatus 10.
It is an object of the present invention to prevent unauthorized copying of video data transmitted from an MPEG-2 decoder to a format encoder.
The video playback apparatus according to the present invention comprises a playback decoder for decoding video data encoded by a predetermined encoding system; a display encoder for encoding the decoded video data into a display signal to be output to a display device; format setting means for setting a data format for the video data to be transmitted from the playback decoder to the display encoder; and format changing means for changing the data format set by the format setting means. The data format of the video data transmitted from the playback decoder to the display encoder can be selected from a plurality of data formats by changing the data format set by the format setting means.
The method for playing back video data according to the present invention comprises the steps of setting a data format for video data; decoding the video data encoded by a predetermined encoding system into the video data whose data format is set by the format setting step; encoding the decoded video data into a display signal to be output to a display device; and changing the data format set by the format setting step.
According to the present invention, the data format for video data to be transmitted from the MPEG-2 decoder to the NTSC encoder is dynamically changed by an MPU. This is effective to prevent unauthorized copying of video data.